The purpose of the proposed research is to increase our knowledge of the functional role of peripheral vascular afferents in the neural control of circulation. This work will focus on the venous afferent mechanoreceptive properties and reflex connections to skeletal muscle motoneurons. This proposal is based on the long-standing anatomical description of vascular afferents and associated receptors of several kinds in the walls of peripheral blood vessels; on previous reports of veni-vasomotor reflexes; and on the previous work by the applicant on femoral venous afferent electrophysiological properties, spinal cord projection patterns, and reflex connections to motoneurons. The mechanical response properties of femoral venous afferents will be studied by analysis of saphenous nerve single fiber responses to static and dynamic distentions of a segment of femoral vein (at the origin of the saphenous vein). Femoral venous afferent connections to spinal cord neurons will be mapped by laminar and single unit analysis of activated neurons. The connections to motoneurons will be studied by condition-test analysis and intracellular recording from motoneurons. Patterns of skeletal muscle activation by electrical and mechanical activation of femoral venous afferents will be examined by analyis of EMG activity in several hindlimb muscles. The results of the proposed work will provide a substantial basis for establishing reflex elicited skeletal "muscle pumping", and greatly extend consideratton of the peripheral vasculature afferents in the neural control of circulation.